The present invention relates to liquid transport members useful for a wide range of applications requiring high flow and/or flux rate, wherein the liquid can be transported through such a member, and/or be transported into or out of such a member. Such members are suitable for many applications, asxe2x80x94without being limited toxe2x80x94disposable hygiene articles, water irrigation systems, spill absorbers, oil/water separators and the like. The invention further relates to liquid transport systems comprising said liquid transport members and articles utilizing these.
The need to transport liquids from one location to another is a well known problem.
Generally, the transport will happen from a liquid source through a liquid transport member to a liquid sink, for example from a reservoir through a pipe to another reservoir. There can be differences in potential energy between the reservoirs (such as hydrostatic height) and there can be frictional energy losses within the transport system, such as within the transport member, in particular if the transport member is of significant length relative to the diameter thereof.
For this general problem of liquid transport, there exist many approaches to create a pressure differential to overcome such energy differences or losses so as to cause the liquids to flow. A widely used principle is the use of mechanical energy such as pumps. Often however, it will be desirable to overcome such energy losses or differences without the use of pumps, such as by exploiting hydrostatic height differential (gravity driven flow), or via capillary effects (often referred to as wicking).
In many of such applications, it is desirable to transport the liquids at high rates, i.e. high flow rate (volume per time), or high flux rate (volume per time per unit area of cross-section).
Examples for applications of liquid transport elements or members can be found in fields like water irrigation such as described in EP-A-0.439.890, or in the hygiene field, such as for absorbent articles like baby diapers both of the pull-on type or with fastening elements like tapes, training pants, adult incontinence products, feminine protection devices.
A well known and widely used execution of such liquid transport members are capillary flow members, such as fibrous materials like blotting paper, wherein the liquid can wick against the gravity. Typically such materials are limited in their flow and/or flux rates, especially when wicking height is added as an additional requirement. An improvement particularly towards high flux rates at wicking heights particularly useful for example for application in absorbent articles has been described in EP-A-0.810.078.
Other capillary flow members can be non-fibrous, but yet porous structures, such as open celled foams. In particular for handling aqueous liquid, hydrophilic polymeric foams have been described, and especially hydrophilic open celled foams made by the so called High Internal Phase Emulsion (HIPE) polymerization process have been described in U.S. Pat. No. 5,563,179 and U.S. Pat. No. 5,387,207.
However, in spite of various improvements made on such executions, there is still a need to get significant increase in the liquid transport properties of liquid transport members.
In particular, it would be desired to obtain liquid transport members, that can transport liquid against gravity at very high flux rates.
In situations wherein the liquid is not homogeneous in composition (such as a solution of salt in water), or in its phases (such as a liquid/solid suspension), it can be desired to transport the liquid in its totality, or only parts thereof. Many approaches are well known for their selective transport mechanism, such as in the filter technology.
For example, filtration technology exploits the higher and lower permeability of a member for one material or phase compared to another material or phase. There is abundance of art in this field, in particular also relating to the so called micro-, ultra-, or nano-filtration. Some of the more recent publications are:
U.S. Pat. No. 5,733,581 relating to melt-blown fibrous filter;
U.S. Pat. No. 5,728,292 relates to non-woven fuel filter;
WO-A-97/47375 relating to membrane filter systems;
WO-A-97/35656 relating to membrane filter systems;
EP-A-0.780.148 relating to monolithic membrane structures;
EP-A-0.773.058 relating to oleophilic filter structures.
Such membranes are also disclosed to be used in absorbent systems.
In U.S. Pat. No. 4,820,293 (Kamme) absorbent bodies are disclosed, for being used in compresses, or bandages, having a fluid absorbent substance enclosed in a jacket made of one essentially homogeneous material. Fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body.
Therein, fluid absorbent materials can have osmotic effects, or can be gel-forming absorbent substances enclosed in semipermeable membranes, such as cellulose, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose acetate butyrate, polycarbonate, polyamide, fiberglass, polysulfone, of polytetrafluoroethylene, having pore sizes of between 0.001 xcexcm and 20 xcexcm, preferably between 0.005 xcexcm and 8 xcexcm, especially about 0.01 xcexcm.
In such a system, the permeability of the membrane is intended to be such that the absorbed liquid can penetrate, but such that the absorbent material is retained.
It is therefore desired to use membranes having a high permeability k and a low thickness d, so as to achieve a high liquid conductivity k/d of the layer, as being described herein after.
This can be achieved by incorporation of promoters with higher molecular weight (e.g. polyvinyl pyrrolidone with a molecular weight of 40,000), such that the membranes can have larger pores leading to larger membrane permeability k. The maximum pore size stated therein to be useful for this application is less than 0.5 xcexcm, with pore sizes of about 0.01 xcexcm or less being preferred. The exemplified materials allow the calculation of k/d values in the range of 3 to 7*10xe2x88x9214 m.
As this system is quite slow, the absorbent body can further comprise for rapid discharge of fluids a liquid acquisition means, such as conventional acquisition means to provide interim storage of the fluids before these are slowly absorbed.
A further application of membranes in absorbent packets is disclosed in U.S. Pat. No. 5,082,723, EP-A-0.365.565, or U.S. Pat. No. 5,108,383 (White; Allied-Signal).
Therein, an osmotic promoter, namely a high-ionic strength material such as NaCl, or other high osmolality material like glucose or sucrose is placed inside a membrane such as made from cellulosic films. As with the above disclosure, fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body. When these packets are contacted by aqueous liquids, such as urine, the promoter materials provide an osmotic driving force to pull the liquid through the membranes. The membranes are characterized by having a low permeability for the promoter, and the packets achieve typical rates of 0.001 ml/cm2/min. When calculating membrane conductivity k/d values for the membranes disclosed therein, values of about 1 to 2*10xe2x88x9215 m result. An essential property of membranes useful for such applications is their xe2x80x9csalt retentionxe2x80x9d, i.e. whilst the membranes should be readily penetrable by the liquid, they must retain a substantial amount of the promoter material within the packets. This salt retention requirements provides a limitation in pore size which will limit liquid flux.
U.S. Pat. No. 5,082,723 (Gross et al.) discloses an osmotic material like NaCl which is enclosed by superabsorbent material, such as a copolymer of acrylic acid and sodium acrylate, thereby aiming at improving absorbency, such as enhanced absorptive capacity on a xe2x80x9cgram per gramxe2x80x9d basis and absorption rate.
Overall, such fluid handling members are used for improved absorbency of liquids, but have only very limited fluid transport capability.
Thus, there remains still a need to improve the liquid transport properties, in particular to increase the flow and/or flux rates in liquid transport systems.
Hence it is an object of the present invention to provide a liquid transport member composed of at least two regions exhibiting a difference in permeability.
It is a further object to provide liquid transport members exhibiting improved liquid transport, as expressed in significantly increased liquid flow rates, and especially liquid flux rates, i.e. the amount of liquid flowing in a time unit through a certain cross-section of the liquid transport member.
It is a further object of the present invention to allow such liquid transport against gravity.
It is a further object of the present invention to provide such an improved liquid transport member for fluids with a wide range of physical properties, such as for aqueous (hydrophilic) or non-aqueous, oily or lipophilic liquids.
It is a further object of this invention to provide liquid transport systems, comprising in addition to the liquid transport member a liquid sink and/or liquid source.
It is an even further object of the present invention to provide any of the above objects for being used in absorbent structures, such as can be useful in hygienic absorbent products, such as baby diapers, adult incontinence products, feminine protection products.
It is an even further object of the present invention to provide any of the above objects for use as water irrigation systems, spill absorber, oil absorber, water/oil separators.
The present invention is a liquid transport member which comprises at least one bulk region and a wall region that completely circumscribes the bulk region, and whereby the wall region further comprises at least one inlet port region and at least one outlet port region, whereby the bulk region has an average fluid permeability kb which is higher than the average fluid permeability kp of the port regions. Preferably, the bulk region has a fluid permeability of at least 10xe2x88x9211 m2, or of at least 10xe2x88x928 m2, more preferably of at least 10xe2x88x927 m2, most preferably of at least 10xe2x88x925 m2, and the port regions bulk region have a fluid permeability of at least 10xe2x88x9211 m2, preferably of at least 10xe2x88x928 m2, more preferably of at least 10xe2x88x927 m2, most preferably of at least 10xe2x88x925 m2 
The liquid transport member can have port regions having a ratio of fluid permeability to thickness in the direction of fluid transport, kp/dp of at least 3*10xe2x88x9215 m, preferably of at least 7*10xe2x88x9214 m, more preferably of at least 3*10xe2x88x9210 m, even more preferably of at least 8*10xe2x88x928 m, or even of at least 5*10xe2x88x927 m, and most preferably of at least 10xe2x88x925 m.
In preferred embodiments the present invention is a liquid transport member wherein a first region of the member comprises materials which are in contact with an additional element, which extends into a neighbouring second region without extending the functionality of the first region. A particular embodiment comprises an additional element extending from the wall region into the outer region, preferably having a capillary pressure for absorbing the liquid that is lower than the bubble point pressure of said member. This additional element may comprise a softness layer.
In a further preferred embodiment, the ratio of permeability of the bulk region and the permeability of the port region is at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 100 000.
In yet a further preferred embodiment, the member has a bubble point pressure when measured with water as test liquid having a surface tension of 72 mN/m of at least 1 kPa, preferably of at least 2 ka, more preferably at least 4.5 ka, even more preferably 8.0 kPa most preferably 50 kPa.
In a further preferred embodiment, the port region has a bubble point pressure when measured with water as test liquid having a surface tension of 72 mN/m of at least 1 kPa, preferably of at least 2 kPa, more preferably at least 4.5 kPa, even more preferably 8.0 kPa, most preferably 50 kpa, or when measured with an aqueous test solution having a surface tension of 33 mN/m of at least 0.67 kPa, preferably at least 1.3 kPa, more preferably at least 3.0 kPa, even more preferably at least 5.3 kPa, most preferably at least 33 kPa.
In a particular embodiment, the liquid transport member according to the present invention looses at least 3% of the initial weight liquid, when submitted to the Closed System test, as described hereinafter.
In a further preferred embodiment, the bulk region has a larger average pore size than said port regions, such that the ratio of average pore size of the bulk region and the average pore size of the port region is preferably at least 10, more preferably at least 50, even more preferably at least 100, or even at least 500, and most preferably at least 1000.
In another preferred embodiment, the bulk region has an average pore size of at least 200 xcexcm, preferably at least 500 xcexcm, more preferably of at least 1000 xcexcm, and most preferably of at least 5000 xcexcm.
In another preferred embodiment, the bulk region has a porosity of at least 50%, preferably at least 80%, more preferably at least 90%, even more preferably of at least 98%, and most preferably of at least 99%.
In another preferred embodiment, the port region has a porosity of at least 10%, more preferably at least 20%, even more preferably of at least 30%, and most preferably of at least 50%.
In another preferred embodiment, the port regions have an average pore size of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 50 xcexcm. It is also preferred, that the port regions have a pore size of at least 1 xcexcm, more preferably at least 3 xcexcm.
In another preferred embodiment, the port regions have an average 10 thickness of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 5 xcexcm.
In another preferred embodiment, the bulk regions and the wall regions have a volume ratio (bulk to wall region) of at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 10000.
In another specific embodiment in particular for transporting aqueous liquids, the port region is hydrophilic, and preferably is made of materials having a receding contact angle for the liquid to be transported less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees. Preferably, the port regions do not substantially decrease the liquid surface tension of the liquid that is to be transported.
In another specific embodiment in particular for transporting oily liquids, the port region is oleophilic, and preferably is made of materials having a receding contact angle for the liquid to be transported less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees.
In another specific embodiment, the liquid transport member can be expandable upon contact with, and collapsible upon removal of liquid.
In other specific embodiments, the member can have a sheet-like, or cylindrical shape, optionally the cross-section of the member along the direction of liquid transport is not constant. Further, port regions can have a larger area than the average cross-section of the member along the direction of liquid transport, preferably port regions have an area that is larger than the average cross-section of the member along the direction of liquid transport by at least a factor of 2, preferably a factor of 10, most preferably a factor of 100.
In another specific embodiment, the member comprises bulk or port material which can expand and recollapse during liquid transport, and preferably has a volume expansion factor of at least 5 between the original state and when being activated, i.e. fully immersed in liquid.
In another specific embodiment, the bulk region comprises a material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, or tubes.
In another specific embodiment, the wall region comprises a material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, tubes, woven webs, woven fiber meshes, apertured films, or monolithic films.
In another specific embodiment, the bulk or wall region may an open cell reticulated foam, preferably a foam selected from the group of cellulose sponge, polyurethane foam, HIPE foams.
In another specific embodiment, the liquid transport member comprises fibers, which are made of polyolefins, polyesters, polyamids, polyethers, polyacrylics, polyurethanes, metal, glass, cellulose, cellulose derivatives.
In yet another embodiment, the liquid transport member is made by a porous bulk region that is wrapped by a separate wall region. In a special embodiment, the member may comprise water soluble materials, for example to increase permeability or pore size upon contact with the liquid in the bulk or port regions.
In further specific embodiments, the liquid transport member is initially wetted by or essentially filled with liquid, or is under vacuum.
A liquid transport member can be particularly suitable to transport of water-based liquids, of viscoelastic liquids, or for bodily exudates such as urine, blood, menses, feces or sweat.
A liquid transport member can also be suitable for transport of oil, grease, or other non-water based liquids, and it can be particularly suitable for selective transport of oil or grease, but not water based liquids. In a special application, the port regions may be hydrophobic.
In yet another specific embodiment, the properties or parameter of any of the regions of the member or of the member itself need not to be maintained during the transport of the member from its production to the intended use, but these are established just prior to or at the time of liquid handling. This may be achieved by having an activation of the member, such as contact with the transported liquid, pH, temperature, enzyme, chemical reaction, salt concentration or mechanical activation. The port region may further comprise a stimulus activatable membrane material, such as a membrane changing its hydrophilicity upon a temperature change.
Another aspect of the present invention concerns the combination of a liquid transport member with a source of liquid and/or the sink of liquid, with at least one of these being positioned outside of the member.
In a specific embodiment, a liquid transport system, comprising a liquid transport member according to the present invention, wherein the system has an absorption capacity of at least 5 g/g, preferably at least 10 g/g, more preferably at least 20 g/g, on the weight basis of the sink material when measured in the Demand Absorbency Test.
In yet another specific embodiment, the liquid transport system contains a sink material that has an absorption capacity of at least 10 g/g, preferably at least 20 g/g and more preferably at least 50 g/g on the basis of the weight of the sink material, when submitted to the Teabag Centrifuge Capacity Test. In a further embodiment, the sink material that has an absorbent capacity of at least 5 g/g, preferably at least 10 g/g, more preferably of at least 50 g/g when measured in the Capillary Suction Test at a pressure up to the bubble point pressure of the port region, and which has an absorbent capacity of less than 5 g/g, preferably less than 2 g/g, more preferably less than 1 g/g, and most preferably of less than 0.2 g/g when measured in the Capillary Suction Test at a pressure exceeding the bubble point pressure of the region.
In certain specific embodiments, the liquid transport member also contains superabsorbent materials or foam made according to the High Internal Phase Emulsion polymerization.
An even further aspect of the present invention relates to an article comprising a liquid transport member or a liquid transport system according to the present invention, such as an absorbent article or a disposable absorbent article comprising a liquid transport member. An application, which can particularly benefit from using members according to the present invention is a disposable absorbent hygiene article, such a baby or adult incontinence diaper, a feminine protection pad, a pantiliner, a training pant. Other suitable applications can be found for a bandage, or other health care absorbent systems. In another aspect, the article can be a water transport system or member, optionally combining transport functionality with filtration functionality, e.g. by purifying water which is transported. Also, the member can be useful in cleaning operation, so as by removing liquids or as by releasing fluids in a controlled manner. A liquid transport member according to the present invention can also be a oil or grease absorber, or can be used for separation of oily and aqueous liquids.
Yet another aspect of the present invention relates to the method of making a liquid transport member, wherein the method comprises the steps of
a) providing a bulk or inner material;
b) providing a wall material comprising a port region;
c) completely enclosing said bulk region material by said wall material;
d) providing a transport enablement means selected from d1) vacuum;
d2) liquid filling;
d3) expandable elastics/springs.
Optionally, the method can comprise the step of
e) applying activation means of
e1) liquid dissolving port region;
e2) liquid dissolving expandable elastication/springs.
e3) removable release element;
e4) removable sealing packaging.
In another embodiment, the method may comprise the steps of
a) wrapping a highly porous bulk material with a separate wall material that contains at least one permeable port region,
b) completely sealing the wall region,
and c) evacuating the member essentially of air.
In an further specific embodiment, the method further comprises the step wetting the member, or partially or essentially completely filling the member with liquid.
In an further specific embodiment, the method additionally comprises the step of sealing the member with a liquid dissolvable layer at least in the port regions.